1. Field of the Invention
The present invention relates to a variable valve actuating mechanism for an internal combustion engine. More particularly, the present invention relates to a valve actuating mechanism for a four-stroke engine suitable for vehicles such as motorcycles in which a camshaft includes a pair of cams for each engine valve so that one of the cams is selectively employed for opening and closing operation of the engine valves.
2. Description of the Background Art
There are a number of known valve actuating mechanisms for internal combustion engines. Generally, a valve actuating mechanism includes a rocker arm supported by a rocker arm shaft extending parallel to the camshaft so as to be capable of pivoting about the axis thereof and to be movable in the axial direction.
The rocker arm selectively comes in contact with a selected one of the cams, and pivots in accordance with the rotation of the camshaft to open and close the engine valve. The one of the cams is selectively used for opening and closing the engine valve by moving the rocker arm as needed in the axial direction.
An example of such known valve actuating mechanism for an engine is disclosed in the Japanese Patent Document No. JP-A-2001-20710.
According to the Japanese Patent Document No. JP-A-2001-20710, the movement of the rocker arm in the axial direction is achieved by using the engine oil pressure. However, since the camshaft is in a state of pushing the engine valve downward via the rocker arm (valve-open state) depending on whether the engine valve is opened or closed, there is a problem that a strong force must be applied to the rocker arm.
When an electrical sensor or control is used for moving the rocker arm according to whether the engine valve is opened or closed, there arises a problem that the configuration of the mechanism itself becomes complicated.
The present invention has been made to overcome such drawbacks. Accordingly, it is an object of the present invention to provide a valve actuating mechanism for an engine for operating cams for opening and closing an engine valve by controllably movement of a rocker arm in the direction of an axis of pivotal movement, and in which movement of the rocker arm is enabled based on whether the engine valve is in a opened or a closed state.